Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.98   12.807%   $253.7932   $253.79   $253.80   $253.80  
  Purchase #2 $177.48   9.108%   $193.6449   $193.64   $193.65   $193.60  
  Purchase #3 $176.74   10.491%   $195.2818   $195.28   $195.30   $195.30  
  Purchase #4 $184.95   4.669%   $193.5853   $193.59   $193.60   $193.60  
  Purchase #5 $173.32   10.704%   $191.8722   $191.87   $191.85   $191.90  
  Purchase #6 $75.82   4.255%   $79.0461   $79.05   $79.05   $79.00  
  Purchase #7 $226.85   7.666%   $244.2403   $244.24   $244.25   $244.20  
  7 purchase totals = $1,240.14       $1,351.4638   $1,351.46   $1,351.50   $1,351.40